Fluid pressure braking system



Feb. 18, 1941. I H c SWIFT 2,232,350

I FLUID PRESSURE BRAKING SYSTEM Filfiid SQPt. 26, 1938 O Q M a I Ma i L INVENTOR.

fiaerir CZ JW/Fr X BY 4% ATTORNEY.

Patented Feb. 18, 1941 "UNITED STATES PRESSURE BRAKING SYSTEM Harvey 0. Swift, Detroit; Mich assignor to Hy dranlic Brake Company, Detroit, Mieln, a corporation of California Application September 2c, 1938, Serial No. 231,831

6 Claims. (c1.- so-.-54,.c)

This invention relates to fluid pressure braking systems. An object of the invention is to provide a fluid pressure braking system including a fluid pres- 5 sure producing device operative-to maintain a positive pressure-on the fluid in the system.

Another object of the invention is to provide a fluid pressure system including a fluid pressure producing device operative to maintain a positive pressure on the fluid in the system and to compensate for expansion and contraction of the fluid incident to changes in temperature.

A feature of the invention is a cylinder, 'and'a pi'ston movable in the cylinder for creating pressure having mounted thereon back of its head a loaded annular pistoneifective for maintaining a positive pressure.

Otherobjects and features of the invention will appear from the following description taken in connection with the drawing forming a part of this specification, and in which- Fig. 1 is a schematic view of a fluid pressure braking system embodying the invention} concentrically thereto'and in direct communication therewith and providing at its junction with the large chamber an annular shoulder. 'The' outer end of'the small chamber 24 is closed as by a head 2! provided with a discharge port 30, and arranged in the wall of the large 22 are ports 32 and 34 providing communications between the large chamber and the reservoir it. A fluid pressure .delivery pipe or conduit a suitably connected to the discharge port has 7 branches connected respectively to fluid pressure actuated motors ll preferably arranged in pairs, one pair for actuating brakes associated with the front wheels of a vehicle and another pair for actuating brakes. associated with the rear wheels I the vehicle.

The rakes may be of any conventional type. Preferably each ofthe brakes includes a fixed support or booking plate ll .adapted to be se-" rig. 2 is a vertical sectional view of the fluid cured to an axle or to axlehousing, a rotatable drum 42 associated with the backing plate adapted to be'secured to a wheel, a pair of corresponding interchangeable friction elements or shoes 44 mounted on the backing plate for operation with thedrum, a retractile spring 46 connecting the shoes, and a motor corresponding tothe motors 38 mounted on the backing plate and connected to the shoes and operative to actuate the shoes into engagement with the drum against the resistance of the retractile springs.

A piston. 48 reciprocable in the cylinder 20 is held against displacement by a washer 50 seated on an annular shoulderin the open end of the large chamber and secured in'place by a retaining ring 52 fitted in a groove in the'wall of the cylinder. The piston 48 includes a detachable head 54 movable in the smallchamber 24, a re duced body portion 58 providing in conjunction with the inner wall-of the cylinder an annular chamber 58 communiqatmg with the reservoir as by way of the port. and a skirtiii slidably engaging the inner' wall of the large chamber: 22 and supporting a cup 62 for inhibiting seepage 'offluid from the cylinder.

The head 54 has spaced passages 64 there- .through providing communications between'the annular chamber 5! and that portion of the small chamber 24 forward of the piston. The head 54 also has an extension 66, and sleeved on the extension is a flexible spider 68 yieldingly supporting a sealing cupflli' for control of the passages 64. The extension 66 also has fitted thereon a spring rest 125 and interpowd between this rest and the head 28 'ofthe cylinder is a spring 14 for returningv the piston to its retracted position. An annular piston II slidable on the reduced body portion 56 of "thepiston 48 between the head 54 and the skirt ill ofthe piston 48 divides the annular chamber Ilinto two sections communicating with one-another by way of passages "through the head of the annular piston. A spring It interposed between the skirt 60 and the back of the head of the annular piston serves other end a coupling SI connected to the -open end of the chamber 22 of the cylinder as by a flexible boot for the exclusion of dust and other 7, foreign from the cylinder, and a rod 92 connects the coupling 88 to a foot pedal lever 94 pivoted on a bracket 96 and connected by a retractile spring 88 to a fixed support I88.

In a normal operation, upon depressing the foot pedal lever 94, force is transmitted therefrom through the rod 92 and thrust pin 88 to the piston 48, resulting inwmoving the piston on its compression stroke. During the initial movement of the piston on its compression stroke, pressure created in the chamber 24 seats the sealing cup 18 on the head 84 of the piston against the resistance of the flexible spider 88, and, thereafter, as the piston 48 proceeds on its compression stroke, the fluid in the chamber 24 forward of the piston is displaced therefrom through the discharge port 30 and fluid pressure delivery pipe or conduit and its respective.

48 and return of the piston to its retracted position under the influence of the spring 14.

:As the piston 48 returns to its retracted posi tion, a partial vacuum is created in the chamber 24, resulting in drawing. fluid from the reservoir,

through the port 32, into the annular chamber 58, thence through the passages 18 in the head of the annular piston 18, past the cup 82 on the head of the annular piston, into that portion of the .cylinder between the annular piston and the back of the head 54 of the piston 48, thence through the passages 84 in the head of the piston 48, through the spider 88 and cup into that portion of the chamber 24 forward of the piston 48, completely filling the chamber 24. During this cycle of the operation, fluid is returning to the cylinder or the chamber 24 from the fluid pressure actuated motors 88 and fluid pressure delivery pipes connecting the motors to the chamber 24.

Under this condition, the chamber 24 receives a quantity of fluid in excess of its capacity, and this excess fluid is displaced from the chamber 24 through the sealing cup III, the spider 88 and the passages 84 in the head of the piston 48 into the annular chamber 58, and thence through the port 34 into the reservoir.

Upon completion of the foregoing cycle, the pring 88 urgesthe annular piston 18 forward so that the sealing cup 82 on the head of the annular piston may close the port 34, and that pressure may be imposed on the fluid in the system. The pressure imposed on the fluid is complementary to the load on the spring 88. Due to expansion and contraction of the fluid, incident to temperature changes, the pressure maintained on the fluid is variable. However, the load on the spring 88 is suflicient to maintain a positive pressure on the fluid in the system at all times.

While this invention has been described in connection with certain specific embodiments, the principle involved is susceptible of numerous other applications that will readily occur to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described the various features of the invention, what I claim as new and desire to secure by Letters Patent is:

l. A fluid pressure producing device comprisingacylinder, a piston movable therein for pro-' ducing pressure, means for by-passing fluid past 3. A fluid pressure producing device compris ing a cylinder, 9. piston movable therein for producing pressure, means for by-passing fluid through the head of the piston when-at rest and on its retraction stroke, an annular piston slidably mounted on the body of the piston, and means imposing a load on the annular piston for maintaining a positive pressure on the fluid forward of the'auxiliary piston;

4. A fluid pressure producing device comprising a reservoir, 9. cylinder supplied therefrom, a piston movable in the cylinder for producing pressure having a head and skirt and a reduced body portion between its, head and skirt, means for lay-passing fluid through the head when the tion of the piston, and means imposing a load on= the auxiliary piston to maintain a sure on the fluid in the. cylinder.

5. A fluid pressure producing device comprising a reservoir, 9. cylinder at the base thereof having a large chamber anda relatively'small chamber, a piston movable in the cylinder for producing pressure having a head fitted in the small chamber, a skirt fitted in the large chamber and a reduced body portion between the head and the skirt, means for by-passing fluid through the head of the piston when the piston is at rest and on its retraction stroke, an annular piston slidable on the reduced body portion of the piston, means imposing a load on the annular piston to maintain a positive pressure on the fluid in the cylinder, and means for actuating the piston.

6. A fluid. pressure producing device comprising a reservoir, a cylinder at the base thereof including a large chamber having spaced ports communicating with the reservoir and a relatively small chamber, a piston movable inthe cylinder for producing pressure including a head fitted in the small chamber, a skirt fitted in the large chamber anda reduced body portion between the head and skirt, means for by-passing fluid through the head of the piston when the positive prespiston is at rest and on its retraction stroke, an Y annular piston slidably mounted on the reduced body portion having passages therethrough,'

means carried by the annular piston for control of the passages and of at least one of the ports providing a communication between the large, 

